With regard to a conventional fan, for example, Japanese Patent Laying-Open No. 1-318798 discloses an impeller of a multiblade blower aiming to mitigate wind noise, n sound (n: the number of revolutions) or the like and further to distribute wake flow vortexes (PTL 1). In the impeller of the multiblade blower disclosed in PTL 1, a columnar portion having a diameter greater than a thickness at a tip end of a blade is provided at a tip end of the blade on an outer circumferential side of a fan.
In addition, Japanese Patent Laying-Open No. 5-44686 discloses a highly efficient tangential fan low in noise level (PTL 2). In the tangential fan disclosed in PTL 2, a back side of a blade of an impeller is formed to decrease in thickness toward an outer circumferential side.